The invention relates to a compressor as per the preamble of patent claim 1.
Compressors for compressing refrigerant are used in a wide variety of applications nowadays. This is the case for example in the field of (room) air conditioning and also in the field of cooling an extremely wide variety of goods. The field of (room) air conditioning includes inter alia the air-conditioning of residential and office buildings and the air-conditioning of motor vehicles (for example the air-conditioning of passenger compartments of passenger motor vehicles and the air-conditioning of driver's cabs in trucks) and air-conditioning in the rail field (air-conditioning of trains, trams and the like). In the field of cooling, refrigerant compressors are used inter alia in the field of refrigerated transport (for example cooling of semitrailers of trucks, cooling of rail wagons and the like) and in the static field, for example in the field of supermarket refrigeration (cold counters, cooling of storage halls in supermarkets, and other storage halls).
An example of a refrigerant compressor having a power unit which is arranged in a power unit space which is (partially or else entirely) delimited by a power unit housing can be found in the field of air-conditioning of passenger motor vehicles. The compressors for passenger motor vehicles are usually swashplate-type compressors. In said type, the power unit has a swashplate or pivot ring which is pivotably arranged on a drive shaft which is in operative engagement with an engine.
Due to the fact that the swashplate or the pivot ring which is arranged with pistons arranged in cylinder bores, so as to be pivotable with respect to the drive shaft, the swept volume of the piston and therefore the delivery volume of the compressor can be influenced. The delivery volume or the piston stroke of the compressor can be adjusted by means of the pressure prevailing in the power unit space. To regulate or control the piston stroke, said compressors have a low-pressure fluid connection which places the power unit space in fluid communication with a suction gas volume in the form of a suction chamber, and a high-pressure fluid connection which places the power unit space in fluid communication with a high-pressure volume (pressure chamber). In this way, refrigerant can be supplied at high pressure to the power unit space via the high-pressure fluid connection, as a result of which the power unit space pressure is increased. The pressure in the power unit space can be reduced via the low-pressure fluid connection.
The known swashplate-type compressors are oil-lubricated compressors. The rotational movement of the swashplate, the movement of other moving components and the pressure changes cause oil situated in the power unit space to be stirred up and form an oil mist (oil mist lubrication). The oil mist formed in the power unit space is transferred via the low-pressure fluid connection (between power unit space and suction chamber) into the suction chamber and from there, together with the refrigerant, into the cylinders. After compression, the oil mist is delivered partially via the high-pressure fluid connection back into the power unit space, while further parts of the oil pass back into the suction gas volume or the suction chamber via a refrigerant circuit of a refrigerant plant in which the compressor is arranged (in particular via cold or heat exchangers which are arranged in the refrigerant circuit and which take the form of a condenser and an evaporator, and via an expansion member arranged in the circuit). Here, to ensure reliable lubrication, the oil is pumped in the circuit. Refrigerant compressors of this type have an oil filling of approximately 100 g of oil per 1 liter of refrigerant.
It is also the case in compressors which are not of swashplate type (for example compressors with constant piston stroke) that oil passes into the refrigerant circuit and from there back into the suction chamber of the compressor, although in said compressors there is generally no fluid connection between the suction chamber and power unit space.
Compressors for the air-conditioning of passenger compartments of passenger motor vehicles are a mass product which is exchanged in the event of a defect. Repairs are not carried out. Likewise, no maintenance is carried out over the service life of a compressor of said type. This is however not the case in the field of compressors of relatively high refrigeration power. While compressors in passenger motor vehicles have relatively low operating durations, larger compressors for example in buses or for cooling goods in trucks and storage halls are in virtually uninterrupted operation. Owing to the high operating durations, regular maintenance of the compressor is essential. An oil change is also carried out during the regular maintenance work. If oil is present throughout the refrigerant circuit, a part of the old oil remains in the compressor or in the refrigeration plant during the oil change. This would shorten the maintenance intervals. Furthermore, the oil present throughout the refrigerant circuit has disadvantages from an energy aspect; such disadvantages are not of significance in the field of passenger motor vehicle air conditioning, but cause energy losses in the case of larger compressors.